They had the best technology NASA had available in the 1970s when they were launched. The spacecraft we are launching more recently, such as New Horizons (the one that just went by Pluto), are considerably more advanced. Voyager's power source consists of a block of plutonium that is more radioactive even than normal plutonium, and which generates heat through radioactive decay. This heat is used to power the spacecraft. As it decays, the probes have less and less power, and will eventually no longer be able to send messages.

I don't know how the antenna that is used to send radio signals sends a tight beam to Earth, but certainly we can still see it.